Scanners have proven useful in allowing the electronic capture of images. Various types of scanners are known, including flatbed, drum, and handheld scanners. Some scanners include automatic document feeders to enable rapid and efficient scanning of multiple documents. Some characteristics[AH1] of a scanner, however, are most useful when appropriately calibrated. For example, scanning is most efficient when a region scanned corresponds closely to an actual extent of the object being scanned. Hence, it may be desirable to calibrate the characteristic corresponding to the lateral and longitudinal positioning of the scanning region relative the object being scanned.
For example, in a scanner with an automatic document feeder, the lateral position or alignment of the document being scanned relative to the scan head depends on mechanical tolerances in the document feeder and the position of the scan head. The alignment may need to be calibrated at initial manufacturing. Furthermore, the alignment can change with time due to wear and drift of components or due to servicing of the scanner. Calibration of this alignment characteristic may therefore be desirable.
Similarly, longitudinal positioning can depend on the relative timing of the document edges (leading and/or trailing) passing the scanning head. For example, in an automatic document feeder, there may be a media sensor separate from the scan head for triggering the start or end of scanning. Often, the media sensor is a mechanical or photoelectric detector. Timing between the media sensor and scan head may be dependent on the mechanical tolerances in the document feeder and the characteristics of the medium. For example, the rate at which media is fed through the document feeder will vary depending on mechanical wear and tolerances in the document feeder as well as the thickness, surface roughness, and other characteristics of the media. Calibration of these timing characteristics may also be desirable.
Hence, it is often desirable to perform calibration on a scanner to correct for positioning and timing errors.